• Title/Summary/Keyword: Water Flows

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A RANS modeling of backward-facing step turbulent flow in an open channel (개수로에서의 후향단차 난류 흐름 RANS 수치모의)

  • Kim, Byungjoo;Paik, Joongcheol
    • Journal of Korea Water Resources Association
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    • v.55 no.2
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    • pp.147-157
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    • 2022
  • The backward-facing step (BFS) is a benchmark geometry for analyzing flow separation occurred at the edge and resulting development of shear layer and recirculation zone that are occupied by turbulent flow. It is important to accurately reproduce and analyze the mean flow and turbulence statistics of such flows to design physically stable and performance assurance structure. We carried out 3D RANS computations with widely used, two representative turbulence models, k-ω SST and RNG k-ε, to reproduce BFS flow at the Reynolds number of 23,000 and the Froude number of 0.22. The performance of RANS computations is evaluated by comparing numerical results with an experimental measurement. Both RANS computations with two turbulence models appear to reasonably well reproduce mean flow in the shear layer and recirculation zone, while RNG k-ε computation results in about 5% larger velocity between the outer edge of boundary layer and the free surface above the recirculation zone than k-ω SST computation and experiment. Both turbulence models underestimate the shear stress distribution experimentally observed just downstream of the sharp edge of BFS, while shear stresses computed in the boundary layer downstream of reattachment point are agree reasonably well with experimental measurement. RNG k-ε modeling reproduces better shear stress distribution along the bottom boundary layer, but overestimates shear shear stress in the approaching boundary layer and above the bottom boundary layer downstream of the BFS.

Simulating inundation depth and area in paddy fields considering back flows (역류를 고려한 논 침수 모의 해석 방법)

  • Noh, Jaekyoung
    • Proceedings of the Korea Water Resources Association Conference
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    • 2021.06a
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    • pp.31-31
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    • 2021
  • 2020년 8월 7일부터 8월 8일까지 호우는 용담댐, 섬진강댐, 합천댐 등 하류 유역의 농경지에 막대한 침수피해를 일으켰다. 특히 논의 인삼재배 지역은 피해가 컸다. 지역에 따라 내수유입, 제방월류, 배수로 역류, 용수로 유입 등 유입량 과다의 침수 현상을 나타냈다. 여기서 이들 다양한 유입량 요소를 고려하여 제내지의 침수심, 침수면적을 모의할 수 있는 물수지 모형을 구축하였고, 하천 수위관측자료가 있는 금산 지역에 적용한 예를 제시하고자 한다. 물수지 모형의 구성은 저류량은 유입량과 방류량으로 구성되며, 유입량은 자체유입, 용수로 유입, 배수로 역류, 제방월류 등으로 구성하였고, 용수로, 배수로의 수문은 원형, 구형 두 가지로 개도에 따라 오리피스 공식을 적용하는 것으로, 제방월류는 여수로 공식의 계수를 조정 적용하는 것으로 하였다. 제내지 내용적은 1:1,000 지형도에서 DEM 자료를 추출하여 생성하였고, 자체유입량은 ONE 모형에 의해 10분 단위로 모의하는 것으로 하였다. 모형 적용 결과는 제원리 제내지 경우이며, 8월 6일 부터 8월 10일 까지 유역면적 322.1ha인 제내지의 10분 간격 물수지 분석 결과, 현장의 침수흔적 조사의 최고수위가 일치하도록 배수문과 배수통관의 방류시 개도율을 조정하며 분석하였다. 이 상태의 침수위 모의 분석결과는 월류고 EL.133.86 m, 월류길이 29m로 나타났다. 10분 최대 강우량 9mm, 1시간 최대 강우량 19mm, 총 강우량 225mm(724,725m3)였고, 10분 최대 유입량 5.619m3/s(3,371m3), 평균 1.264m3/s(758m3), 총545,933m3였다. 용수로 유입은 없었고, 배수문 역류 유입량은 13시간 50분 동안, 10분 최대 6,836m3, 총 28.26만m3였고, 제방월류 유입량은 9시간 30분 동안, 10분 최대 7,212m3, 총 33.15만m3였고, 배수문 방류량은 3일 20시간 20분 동안, 10분 최대 19,932m3, 총 116.13만m3였다. 하천수위는 최고 EL.134.45m, 최소 EL.128.51m, 평균 EL.130.69m였고, 내수위는 최고 EL.134.05m, 최소 EL.129.00m, 평균 EL.131.02m였다. 최고 침수위 EL.134.05m일 때 DEM으로부터 침수면적은 38.88ha로 분석되었다. 내수 유입에 의한 침수면적 19.54ha를 빼면 10.71ha가 배수문과 제방월류를 통해 유입된 수량으로 침수된 것으로 분석되었다.

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Measurement of the Equivalent Resistance Coefficient for Multi-piers in Open Channel (개수로 다열기둥에 대한 상당저항계수의 측정)

  • Kwon, Kab Keun;Choi, Junwoo;Yoon, Sung Bum
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.28 no.6B
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    • pp.635-642
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    • 2008
  • The influence of unsubmerged resistance bodies in a channel turbulence flow on energy loss was investigated by hydraulic experiments. Square-shaped multi-piers were used for unsubmerged structure or rigid vegetation in an open channel. In experimental channel flows multi-piers were arranged in double or single row along the channel direction, and mean-concept uniform elevations were attained and measured with a set of discharges and channel slopes. Applying the experimental results to the Manning equation, the equivalent resistance coefficient n, which implicates flow resistance and energy loss due to bottom friction as well as drag, was evaluated with varying the interval of piers and the uniform water depth. And the experimentally evaluated n values were compared with the semi-theoretical formula of the equivalent resistance coefficient derived from momentum analysis including a drag interaction coefficient. From the comparisons it was found that the interaction effect of piers on flow resistance was significant for the overall energy losses in a channel flow. The n values decrease when the interval of piers in flow-direction is less than about 2.2 times of the pier width. And it was also found that the n values increase with the 2/3 power of water depth in the theoretical formula, since the drag interaction coefficient was found to be mostly dependent on the interval of piers.

Spatial Structure and Seasonal Variation of Temperature and Salinity in the Early Stage of Reclaimed Brackish Lake (Hwaong Reservoir) (간척호 (화옹호) 생성 초기의 수온과 염분의 공간적 구조와 계절적 변화)

  • Shin, Jae-Ki;Yoon, Chun-Gyeong;Hwang, Soon-Jin
    • Korean Journal of Ecology and Environment
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    • v.39 no.3 s.117
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    • pp.352-365
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    • 2006
  • In order to evaluate the change of aquatic environment in the reclaimed Hwaong Reservoir, situated in the early stage after construction, this study was conducted to measure the change of precipitation, temperature, and salinity from June 2002 to January 2006. The range and mean of temperature was $-0.7{\sim}33.4^{\circ}C$ and $13.6^{\circ}C$, respectively. Temperature of upstream part rapidly changed during the transitional period; from spring to summer and from fall to winter. It showed abrupt decrease with high discharge from the streams temporarily. While, hypolimnetic temperature of upstream happened to be somewhat higher than that of surface or downstream. The range and mean of salinity was 0.3${\sim}$32.3 psu and 25.3 psu, respectively. Vertical difference of salinity was marked, and the change in the surface water was much higher than middle or bottom layers. It showed the marked difference at all stations, except for the bottom layer of upstream into which Namyang Stream flows, indicating that vertical gradient of salinity is strongly sustained in the reservoir. Salinity was changed markedly during the storm period (June${\sim}$October), and freshwater with low salinity was expanded from upstream to downstream along the surface layer. The surface of the reservoir was totally covered by the stream discharged water with a large amount of silt and low salinity during this period. The difference of temperature and salinity between the surface and bottom layer ranged $-10.6{\sim}9.7^{\circ}C$ and $-27.1{\sim}30.0$ psu, respectively. The big difference of salinity appeared with a large discharge of freshwater from the streams or large input of seawater through the gate. Salinity was negatively correlated with temperature, indicating the influence of monsoon storm events on the salinity under the whole watershed scale of this brackish reclaimed reservoir.

Assessing the Benefits of Incorporating Rainfall Forecasts into Monthly Flow Forecast System of Tampa Bay Water, Florida (하천 유량 예측 시스템 개선을 위한 강우 예측 자료의 적용성 평가: 플로리다 템파 지역 사례를 중심으로)

  • Hwang, Sye-Woon;Martinez, Chris;Asefa, Tirusew
    • Journal of The Korean Society of Agricultural Engineers
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    • v.54 no.4
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    • pp.127-135
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    • 2012
  • This paper introduced the flow forecast modeling system that a water management agency in west central Florida, Tampa Bay Water has been operated to forecast monthly rainfall and streamflow in the Tampa Bay region, Florida. We evaluated current 1-year monthly rainfall forecasts and flow forecasts and actual observations to investigate the benefits of incorporating rainfall forecasts into monthly flow forecast. Results for rainfall forecasts showed that the observed annual cycle of monthly rainfall was accurately reproduced by the $50^{th}$ percentile of forecasts. While observed monthly rainfall was within the $25^{th}$ and $75^{th}$ percentile of forecasts for most months, several outliers were found during the dry months especially in the dry year of 2007. The flow forecast results for the three streamflow stations (HRD, MB, and BS) indicated that while the 90 % confidence interval mostly covers the observed monthly streamflow, the $50^{th}$ percentile forecast generally overestimated observed streamflow. Especially for HRD station, observed streamflow was reproduced within $5^{th}$ and $25^{th}$ percentile of forecasts while monthly rainfall observations closely followed the $50^{th}$ percentile of rainfall forecasts. This was due to the historical variability at the station was significantly high and it resulted in a wide range of forecasts. Additionally, it was found that the forecasts for each station tend to converge after several months as the influence of the initial condition diminished. The forecast period to converge to simulation bounds was estimated by comparing the forecast results for 2006 and 2007. We found that initial conditions have influence on forecasts during the first 4-6 months, indicating that FMS forecasts should be updated at least every 4-6 months. That is, knowledge of initial condition (i.e., monthly flow observation in the last-recent month) provided no foreknowledge of the flows after 4-6 months of simulation. Based on the experimental flow forecasts using the observed rainfall data, we found that the 90 % confidence interval band for flow predictions was significantly reduced for all stations. This result evidently shows that accurate short-term rainfall forecasts could reduce the range of streamflow forecasts and improve forecast skill compared to employing the stochastic rainfall forecasts. We expect that the framework employed in this study using available observations could be used to investigate the applicability of existing hydrological and water management modeling system for use of stateof-the-art climate forecasts.

Variation of Air Temperature Inside Carbonate Area Caves (석회암 지역에 분포하는 동굴의 내부 온도 변동 특성)

  • Kim, Lyoun;Park, Youngyun;Lee, Jonghee;Choi, Jaehun;Jung, Qyusung;Kim, Jungtae;Kim, Insu
    • Korean Journal of Heritage: History & Science
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    • v.53 no.1
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    • pp.52-63
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    • 2020
  • This study was conducted in order to evaluate the characteristics of air temperature fluctuation inside the Daegeumgul, Ondaldonggul, and Seongnyugul Caves, which are the most representative limestone caves in Korea, and also to assess the effects of air temperature on cave temperature. Temperature was measured hourly at three sites in Daegeumgul, Ondaldonggul, and Seongnyugul Caves from April 13 to June 25, 2019. Additionally, air temperature data for the areas around the caves was provided by the Meteorological Administration. Using this collected data, the basic statistical measure of fluctuation characteristics over time was ascertained, and time series analyses were performed. Wide variation of temperature was exhibited in the order of the cave entrance, the cave water inflow point, and the midpoint. Cave temperature was observed to increase gradually during the study period. There was a vast range in temperature at the Daegeumgul station located approximately 150 m outside the cave, but it remained nearly constant beyond the midpoint. Although the effect of air temperature was not significant due to the influence of visitors, the effect of air temperature on cave temperature gradually decreased from the entrance to the interior. At Ondaldonggul, there was a wide range in temperature recorded at the entrance due to the influence of air temperature, but it stayed almost constant in the interior. However, at the site where cave water flows into the cave, temperature was influenced by the cave water temperature. At Seongnyugul, there was a distinct fluctuation in temperature recorded at the cave entrance, while the middle of the cave remained nearly constant. Temperature fluctuated due to the air temperature at the entrance, while at the middle of the cave, measurements were expected to be affected to a greater extent by the lake water temperature than by the air temperature. However, this pattern was not observed. According to the time series analysis results, in all caves, fluctuations of air temperature affected cave temperature after approximately one hour. Cave size and structure, water presence, the entrance's size and shape, air flow, and visitor patterns can all influence cave temperature. Therefore, consideration of these factors is very important in the pursuit to clearly understand cave temperature characteristics.

Recent Progress in Air-Conditioning and Refrigeration Research : A Review of Papers Published in the Korean Journal of Air-Conditioning and Refrigeration Engineering in 2013 (설비공학 분야의 최근 연구 동향 : 2013년 학회지 논문에 대한 종합적 고찰)

  • Lee, Dae-Young;Kim, Sa Ryang;Kim, Hyun-Jung;Kim, Dong-Seon;Park, Jun-Seok;Ihm, Pyeong Chan
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.26 no.12
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    • pp.605-619
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    • 2014
  • This article reviews the papers published in the Korean Journal of Air-Conditioning and Refrigeration Engineering during 2013. It is intended to understand the status of current research in the areas of heating, cooling, ventilation, sanitation, and indoor environments of buildings and plant facilities. Conclusions are as follows. (1) The research works on the thermal and fluid engineering have been reviewed as groups of fluid machinery, pipes and relative parts including orifices, dampers and ducts, fuel cells and power plants, cooling and air-conditioning, heat and mass transfer, two phase flow, and the flow around buildings and structures. Research issues dealing with home appliances, flows around buildings, nuclear power plant, and manufacturing processes are newly added in thermal and fluid engineering research area. (2) Research works on heat transfer area have been reviewed in the categories of heat transfer characteristics, pool boiling and condensing heat transfer and industrial heat exchangers. Researches on heat transfer characteristics included the results for general analytical model for desiccant wheels, the effects of water absorption on the thermal conductivity of insulation materials, thermal properties of Octadecane/xGnP shape-stabilized phase change materials and $CO_2$ and $CO_2$-Hydrate mixture, effect of ground source heat pump system, the heat flux meter location for the performance test of a refrigerator vacuum insulation panel, a parallel flow evaporator for a heat pump dryer, the condensation risk assessment of vacuum multi-layer glass and triple glass, optimization of a forced convection type PCM refrigeration module, surface temperature sensor using fluorescent nanoporous thin film. In the area of pool boiling and condensing heat transfer, researches on ammonia inside horizontal smooth small tube, R1234yf on various enhanced surfaces, HFC32/HFC152a on a plain surface, spray cooling up to critical heat flux on a low-fin enhanced surface were actively carried out. In the area of industrial heat exchangers, researches on a fin tube type adsorber, the mass-transfer kinetics of a fin-tube-type adsorption bed, fin-and-tube heat exchangers having sine wave fins and oval tubes, louvered fin heat exchanger were performed. (3) In the field of refrigeration, studies are categorized into three groups namely refrigeration cycle, refrigerant and modeling and control. In the category of refrigeration cycle, studies were focused on the enhancement or optimization of experimental or commercial systems including a R410a VRF(Various Refrigerant Flow) heat pump, a R134a 2-stage screw heat pump and a R134a double-heat source automotive air-conditioner system. In the category of refrigerant, studies were carried out for the application of alternative refrigerants or refrigeration technologies including $CO_2$ water heaters, a R1234yf automotive air-conditioner, a R436b water cooler and a thermoelectric refrigerator. In the category of modeling and control, theoretical and experimental studies were carried out to predict the performance of various thermal and control systems including the long-term energy analysis of a geo-thermal heat pump system coupled to cast-in-place energy piles, the dynamic simulation of a water heater-coupled hybrid heat pump and the numerical simulation of an integral optimum regulating controller for a system heat pump. (4) In building mechanical system research fields, twenty one studies were conducted to achieve effective design of the mechanical systems, and also to maximize the energy efficiency of buildings. The topics of the studies included heating and cooling, HVAC system, ventilation, and renewable energies in the buildings. Proposed designs, performance tests using numerical methods and experiments provide useful information and key data which can improve the energy efficiency of the buildings. (5) The field of architectural environment is mostly focused on indoor environment and building energy. The main researches of indoor environment are related to infiltration, ventilation, leak flow and airtightness performance in residential building. The subjects of building energy are worked on energy saving, operation method and optimum operation of building energy systems. The remained studies are related to the special facility such as cleanroom, internet data center and biosafety laboratory. water supply and drain system, defining standard input variables of BIM (Building Information Modeling) for facility management system, estimating capability and providing operation guidelines of subway station as shelter for refuge and evaluation of pollutant emissions from furniture-like products.

Seasonal and Inter-annual Variability of Water Use Efficiency of an Abies holophylla Plantation in Korea National Arboretum (국립수목원의 전나무(Abies holophylla) 조림지의 물 이용 효율의 계절 및 경년 변동)

  • Thakuri, Bindu Malla;Kang, Minseok;Zhang, Yonghui;Chun, Junghwa;Kim, Joon
    • Korean Journal of Agricultural and Forest Meteorology
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    • v.18 no.4
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    • pp.366-377
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    • 2016
  • Water use efficiency (WUE) is considered as an important ecological indicator which may provide information on the process-structure relationships associated with energy-matter-information flows in ecosystem. The WUE at ecosystem-level can be defined as the ratio of gross primary productivity (GPP) to evapotranspiration (ET). In this study, KoFlux's long-term (2007-2015) eddy covariance measurements of $CO_2$ and water vapor fluxes were used to examine the WUE of needle fir plantation in Korea National Arboretum. Our objective is to ascertain the seasonality and inter-annual variability in WUE of this needle fir plantation so that the results may be assimilated into the development of a holistic ecological indicator for resilience assessment. Our results show that the WUE of needle fir plantation is characterized by a concave seasonal pattern with a minimum ($1.8-3.3g\;C{\cdot}(kg\;H_2O)^{-1}$) in August and a maximum ($5.1-11.4g\;C{\cdot}(kg\;H_2O)^{-1}$) in February. During the growing season (April to October), WUE was on average $3.5{\pm}0.3g\;C\;(kg\;H_2O)^{-1}$. During the dormant seasons (November to March), WUE showed more variations with a mean of $7.4{\pm}1.0g\;C{\cdot}(kg\;H_2O)^{-1}$. These values are in the upper ranges of WUE reported in the literature for coniferous forests in temperate zone. Although the growing season was defined as the period from April to October, the actual length of the growing season (GSL) varied each year and its variation explained 62% of the inter-annual variability of the growing season WUE. This is the first study to quantify long-term changes in ecosystem-level WUE in Korea and the results can be used to test models, remote-sensing algorithms and resilience of forest ecosystem.

SOME PHYSICAL OCEANOGRAPHIC RESEARCH ON KWANG YANG BAY ( I ) (광양만의 물리적 해황에 관한 연구 ( I ))

  • 장지원
    • Journal of the Korean Society of Fisheries and Ocean Technology
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    • v.10 no.1
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    • pp.1-18
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    • 1974
  • Some coastal oceanographic investigations in Kwang Yang Bay were carried out bimonthly from April to September (The first half period of the research project) in 1974. The behaviour of the waters, distributions of water temperature and salinity and diffusion characteristic by dye release experiments in the bay are studied for the problems of practical importance in connection with water pollution. Velocities and directions of tidal currents at five fixed stations were observed. And dye diffusion experiment was also carried out on the sea. According to the results from this study, the salinity of the water is lower, ranging from about $28\;\textperthousand\;to\;32\textperthousand$, on all over the surface in the bay with the cause that the fresh water flows in from the Sumjin river. Diffusivities in this sea by means of Rhodamine B diffusion elliperiment were $785.6\;{\times}\;10^2\;\textrm{m}^2/sec$ in major axis, $15.6\;{\times}\;10^2 \;\textrm{m}^2/sec$/sec in minor axis in the direction on patch after 30 minutes from the dye release.

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Analysis of Fluid Flows in a High Rate Spiral Clarifier and the Evaluation of Field Applicability for Improvement of Water Quality (고속 선회류 침전 장치의 유동 해석 및 수질 개선을 위한 현장 적용 가능성 평가)

  • Kim, Jin Han;Jun, Se Jin
    • Journal of Wetlands Research
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    • v.16 no.1
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    • pp.41-50
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    • 2014
  • The purpose of this study is to evaluate the High Rate Spiral Clarifier(HRSC) availability for the improvement of polluted retention pond water quality. A lab scale and a pilot scale test was performed for this. The fluid flow patterns in a HRSC were studied using Fluent which is one of the computational fluid dynamic(CFD) programs, with inlet velocity and inlet diameter, length of body($L_B$) and length of lower cone(Lc), angle and gap between the inverted sloping cone, the lower exit hole installed or not installed. A pilot scale experimental apparatus was made on the basis of the results from the fluid flow analysis and lab scale test, then a field test was executed for the retention pond. In the study of inside fluid flow for the experimental apparatus, we found out that the inlet velocity had a greater effect on forming spiral flow than inlet flow rate and inlet diameter. There was no observable effect on forming spiral flow LB in the range of 1.2 to $1.6D_B$(body diameter) and Lc in the range of 0.35 to $0.5L_B$, but decreased the spiral flow with a high ratio of $L_B/D_B$ 2.0, $Lc/L_B$ 0.75. As increased the angle of the inverted sloping cone, velocity gradually dropped and evenly distributed in the inverted sloping cone. The better condition was a 10cm distance of the inverted sloping cone compared to 20cm to prevent turbulent flow. The condition that excludes the lower exit hole was better to prevent channeling and to distribute effluent flow rate evenly. From the pilot scale field test it was confirmed that particulate matters were effectively removed, therefore, this apparatus could be used for one of the plans to improve water quality for a large water body such as retention ponds.